Method of making components with releasable leads

ABSTRACT

A connection component for making connections to a microelectronic element is made by providing leads on a surface of a polymeric layer and etching the polymeric layer to partially detach the leads from the polymeric layer, leaving a portion of each lead releasably connected to the polymeric layer by a small polymeric connecting element which can be broken or peeled away from the lead. Leads in a connecting element may be covered by an insulating jacket applied by a coating process, and the insulating jacket may in turn be covered by a conductive layer so that each lead becomes a miniature coaxial cable. This arrangement provides immunity to interference and facilitates operation at high speeds.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/366,425, filed Feb. 13, 2003, now U.S. Pat. No. 6,763,579which application is a divisional of U.S. patent application Ser. No.09/549,638, filed Apr. 14, 2000, now U.S. Pat. No. 6,557,253, which is acontinuation of U.S. patent application Ser. No. 09/020,750, filed Feb.9, 1998, now abandoned the disclosure of which is hereby incorporated byreference herein.

FIELD OF THE INVENTION

The present invention relates to components useful in making electricalconnections to microelectronic elements such as semiconductor chips, andto methods of manufacturing such components.

BACKGROUND OF THE INVENTION

Certain techniques for making semiconductor chip assemblies and similarmicroelectronic assemblies employ releasably attached leads. One suchprocess is disclosed in commonly assigned U.S. Pat. No. 5,518,964, thedisclosure of which is hereby incorporated by reference herein. Incertain preferred embodiments described in the '964 patent, a firstelement such as a dielectric layer in a connection component is providedwith a plurality of elongated, flexible leads extending along a surfaceof the element. Each lead has a terminal end permanently attached to thefirst element and has a tip end offset from the terminal end. The tipends of the leads may be releasably secured to the first element. Asecond element such as a semiconductor chip having contacts thereon isengaged with the first element or connection component, and the tip endsof the leads are bonded to contacts on the chip or second element. Theelements are then moved away from one another so as to deform the leadsand provide vertically extensive leads extending between the first andsecond elements, i.e., between the chip and the connection component. Acompliant material may be introduced between the chip and the connectioncomponent.

The resulting structure allows the chip to move relative to theconnection component without substantial stresses on the leads, and thusprovides compensation for thermal expansion. The preferred structurescan be readily tested and can be mounted on a further substrate such asa printed circuit panel or the like. Preferred embodiments of theprocesses disclosed in the '964 patent can be used with chips or othermicroelectronic elements having large numbers of terminals. In thepreferred processes, many leads can be deformed simultaneously. Inparticularly preferred processes according to the '964 patent, the leadson a given connection component or first element may be connected tocontacts on a plurality of chips such as an array of several chips ornumerous chips formed as part of a wafer, so that many leads aredeformed simultaneously.

In certain embodiments disclosed in the '964 patent, the tip end of eachlead is bonded to the surface of the first element by a small spot of abase metal such as copper interposed between the tip end and thesurface. Typically, such a spot is formed by a process in which theleads are formed from an etch-resistant metal such as gold overlying acontinuous layer of the base metal. The leads have wide portions at thetip and terminal ends. The component is then subjected to an etchingprocess, as by exposing the component to a liquid etch solution whichattacks the base metal so as to undercut the lead and remove the basemetal from beneath the etch-resistant metal at all locations except atthe terminal end and at the tip end. At the tip end, most, but not allof the base metal is removed from beneath the etch-resistant metal,leaving a very small spot of the base metal. The strength of the bondbetween the tip and the connection component surface is effectivelycontrolled by the size of the spot. Thus, although the base metal mayprovide a relatively high bond strength per unit area or per unitlength, it may still provide a weak attachment of the tip end of thelead end to the first element surface. Although structures such asfrangible lead sections and small buttons can provide useful releasableattachments for the tip ends of the leads, some care is required infabrication to form these features. Formation of spots of base metal ofuniform size beneath the terminal ends of leads on a large connectioncomponent requires control of the etching process. Moreover, anyvariation in the strength of the bond between the base metal and thesurface will result in a corresponding variation in the strength withwhich the tip ends of the leads are held to the surface.

As described in PCT International Publication WO 94/03036, thedisclosure of which is hereby also incorporated herein by reference, aconnection component may incorporate a support structure such as apolyimide or other dielectric layer with one or more gaps extendingthrough such layer. Preferably, the support structure incorporates oneor more flexible or compliant layers. The connection component mayfurther include leads extending across the gap. Each lead has a first orterminal end permanently secured to the support structure on one side ofthe gap, and a second end releasably attached to the support structureon the opposite side of the gap. In preferred processes as taught by the'036 publication, the connection component is positioned on asemiconductor chip or other microelectronic element. Each lead isengaged by a bonding tool and forced downwardly into the gap, therebydetaching the releasably connected second end from the supportstructure. The leads are flexed downwardly into the gap and bonded tothe contacts on the chip or the microelectronic element. Preferredconnection components and processes according to the '036 publicationalso provide highly efficient bonding processes and very compactassemblies. The finished products provide numerous advantages such ascompensation for thermal expansion, ease of testing and a compactconfiguration.

Other structures disclosed in the '036 publication and in the '964patent employ frangible lead sections connecting the releasable end ofeach lead to another structure permanently mounted to the supportstructure or first element. Frangible sections can also provide usefulresults. However, such frangible elements are most commonly formed byusing the photo-etching or selective deposition processes used to formthe lead itself to form a narrow section. The minimum width at thenarrow section, can be no less than the smallest width formable in theprocess. As the other portions of the lead adjacent the narrow sectionmust be wider than the narrow section, these other portions must belarger than the minimum attainable in the process. Stated another way,the leads made by such a process generally are wider than the minimumline width attainable in the formation process. This limits the numberof leads which can be accommodated in a given area.

In other embodiments disclosed in the '036 publication, the first orpermanently mounted terminal end of a lead may have a relatively largearea, whereas the second or releasably mounted end of the lead overlyingthe support structure may have a relatively small area, so that suchsecond end will break away from the support structure before the firstend when the lead is forced downwardly by the bonding tool. Thisarrangement requires control of the dimensions of the ends to controlthe area of the bond between the lead end and the support structure andalso requires a lead wider than the smallest element formable in theprocess.

As described in the '036 publication, and as further described incommonly assigned International Publication WO 97/11588, the disclosureof which is also incorporated by reference herein, leads used in theseand other microelectronic connection components may include polymericlayers in addition to metallic layers. The polymeric layers structurallyreinforce the leads. For example, certain leads described in the '588publication incorporate a pair of thin conductive layers such asmetallic layers overlying opposite surfaces of a polymeric layer. Oneconductive layer may be used as a signal conductor, whereas the oppositeconductive layer may act as a potential reference conductor. Thecomposite lead thus provides a stripline extending along the lead. Astripline lead of this nature can provide a low, well-controlledimpedance along the lead, which enhances the speed of operation of thecircuit formed by the connection component and the associatedmicroelectronic elements. The potential reference conductor also helpsto reduce crosstalk or undesirable inductive signal coupling betweenadjacent leads.

Despite all of these improvements, still further improvements would bedesirable.

SUMMARY OF THE INVENTION

One aspect of the present invention provides methods of makingconnection components. A method according to this aspect of theinvention desirably includes the steps of providing a starting structureincluding one or more metallic leads overlying a polymeric dielectriclayer, and etching portions of the dielectric layer disposed beneathsaid one or more leads by contacting the starting structure with anetchant, most preferably a gaseous etchant such as a plasma of areactant gas including oxygen or other oxidizing gas. Typically, in thestarting structure the leads overlie a first surface of the dielectriclayer. The etching step may be performed by exposing the first surface,with the leads thereon, to the etchant. The etching step most preferablyis performed so as to leave only certain parts of the said leadsconnected to the dielectric layer by etch-defined polymeric connectionregions smaller than such parts. Thus, after the etching step, the leadsare spaced vertically from the etched surface of the dielectric layer.The connection regions form polymeric connecting elements integral withthe dielectric layer and extending vertically between the dielectriclayer and the overlying regions of the leads, referred to herein as theattachment regions of the leads.

The polymeric connection regions or connecting elements providereliable, readily releasable connections between the attachment regionsof the leads and the dielectric layer. Regardless of the degree ofadhesion between the polymeric layer and the material of the leads, theforce required to release a connection cannot exceed the tensilestrength of the polymeric connecting element. This is controlled by thecross-sectional area of the polymeric connecting element. This area canbe controlled accurately in the etching process.

Each lead may include first and second ends, and an elongated regionextending between these ends. The etching step may be performed so as todetach the elongated region from the dielectric layer, and so as toleave one end of the lead releasably connected to the dielectric layerby such a connecting element. The other end of the lead may be leftpermanently anchored to the dielectric layer. For example, the firstends of the lead and the underlying portion of the polymeric layer maybe covered with a mask during the etching process, so that the polymericlayer remains substantially unetched and the first ends remain securelyanchored to the polymer layer. The second ends of the leads and theunderlying portions of the polymeric layer may be exposed to the etchantso as to remove parts of the polymeric layer and form the polymericconnecting elements beneath the second ends of the leads.

A further aspect of the invention provides a microelectronic connectioncomponent comprising a support structure including a polymericdielectric layer having a surface extending in horizontal directions;one or more metallic conductive structures such as leads overlying saidsurface of said dielectric layer, the conductive structures havingattachment portions vertically spaced from said surface; and polymericconnecting elements integral with said dielectric layer extendingbetween the surface and the attachment portions of said conductivestructures. The attachment portions of the leads overly the polymericconnecting elements. Each such connecting element has at least onehorizontal dimension smaller than the corresponding horizontal dimensionof the attachment portion overlying that connecting element. Theconnecting elements preferably form releasable connections between theattachment portions of the leads and the support structure. Componentsaccording to this aspect of the invention can be fabricated according tothe processes discussed above.

A further aspect of the invention provides methods of makingmicroelectronic connection components comprising the steps of: providinga support structure and one or more leads mounted to said supportstructure; and depositing a dielectric material on the leads. Mostpreferably, the leads are deformable or movable with respect to thesupport structure. The depositing step preferably is performed so thatthe deposited dielectric material provides a continuous jacket extendingentirely around the lead over at least a portion of its length. Forexample, portions of the leads may project from an edge of the supportstructure or project across gaps in the support structure, and acontinuous jacket may be provided in these portions of the lead. Theprocess can provide microscopic leads on connection components withinsulating jackets typically provided only on much larger leads such asconventional wires. The depositing step may be performed by means of anelectrophoretic deposition bath.

According to a further aspect of the invention, the process may includethe additional step of depositing a conductive layer such as a metalliclayer over the deposited dielectric. The metallic layer thus forms areference conductor extending coaxially with the lead but insulatedtherefrom by the dielectric jacket. In effect, each lead is converted toa miniature coaxial cable.

Yet another aspect of the invention provides microelectronic connectioncomponent including a support structure and one or more leads attachedto the support structure. Each lead has an elongated section movablewith respect to the support structure. A jacket of a dielectric materialsurrounds each said lead over at least a part of the elongated sectionof that lead. The component preferably further includes referenceconductors surrounding and extending coaxially with the elongatedsections of said leads and insulated therefrom by the jackets ofdielectric material, the reference conductors including a coating of anelectrically conductive material overlying the dielectric jackets. Theelongated sections of the leads preferably have cross-sectionaldimensions less than about 100μ, and typically about 50μ or less,whereas the dielectric material may be about 12–50 μm thick. Thereference conductors may be electrically connected to potential planeelements on the support structures, such as ground or power planes.

The insulated leads provide immunity to accidental short-circuitingduring or after connection with the microelectronic component. In theembodiment incorporating the conductive jackets, the leads act asminiature coaxial cables, and provide well-controlled impedance whichenhances signal propagation and permits operation at high frequencies.The miniature coaxial cables also provide outstanding immunity toelectromagnetic interference such as cross-talk between adjacent leads.In a further variant, each lead and the surrounding conductive jacketmay serve as the two conductors of a differential signaling circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary elevational view of a connection component inaccordance with one embodiment of the invention during a process ofmanufacturing in accordance with an embodiment of the invention.

FIG. 2 is a diagrammatic sectional view taken along line 2—2 in FIG. 1.

FIG. 3 is a view similar to FIG. 2 but depicting the component in alater stage of the process.

FIG. 4 is a fragmentary, diagrammatic perspective view depicting aportion of the component illustrated in FIG. 3, in a position invertedfrom that shown in FIG. 3.

FIG. 5 is a fragmentary, diagrammatic sectional view taken along line5—5 in FIG. 4.

FIG. 6 is a fragmentary, diagrammatic sectional view taken along line6—6 in FIG. 4.

FIG. 7 is a fragmentary, diagrammatic sectional view taken along line7—7 in FIG. 4.

FIG. 8 is a view similar to FIG. 2 but depicting the component in duringuse, in conjunction with a microelectronic element.

FIG. 9 is a fragmentary diagrammatic perspective view depicting acomponent in a process according to a further embodiment of theinvention.

FIG. 10 is a view similar to FIG. 9 but depicting the component during alater stage of the process.

FIG. 11 is a sectional view taken along line 11—11 in FIG. 10.

FIG. 12 is a fragmentary diagrammatic perspective view depicting acomponent in a process according to yet another embodiment of theinvention.

FIGS. 13 and 14 are views similar to FIG. 12 but depicting the componentof FIG. 12 in later stages of the process.

FIG. 15 is a fragmentary diagrammatic perspective view depicting acomponent in a process according still another embodiment of theinvention.

FIG. 16 is a view similar to FIG. 15 but depicting the component of FIG.15 in a later stage of the process.

FIG. 17 is a fragmentary sectional view taken along line 17—17 in FIG.16.

FIG. 18 is a view similar to FIG. 15 but depicting the component ofFIGS. 15–17 in a later stage of the process.

FIG. 19 is a fragmentary sectional view taken along line 19—19 in FIG.18.

FIG. 20 is a fragmentary diagrammatic perspective view depicting acomponent in accordance with another embodiment of the invention.

FIG. 21 is a view similar to FIG. 20, but depicting a component inaccordance with a further embodiment of the invention, in conjunctionwith a semiconductor chip.

FIG. 22 is a schematic electrical diagram depicting an electricalcircuit in the embodiment of FIG. 21.

FIG. 23 is a diagrammatic plan view depicting a component in accordancewith a further embodiment of the invention.

FIG. 24 is a diagrammatic elevational view of the component depicted inFIG. 23, together with a microelectronic element during successivestages of a process in accordance with yet another embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A process in accordance with one embodiment of the invention begins witha starting structure 20 incorporating a dielectric layer, preferably apolymeric layer 22 and a plurality of leads 24 overlying a surface 26 ofthe dielectric layer. Each lead includes a first end 28, a second end 30and a relatively narrow, elongated section 32 extending between theends. The first end 28 of each lead is wider than elongated section 32,and the second end 30 of each lead is also wider than the elongatedsection. Stated another way, the minimum distance across each lead atthe ends is greater than the minimum distance across the lead withinelongated section 32. The leads adhere to the surface 26 of layer 22.Additionally, the first end 28 of each lead is physically attached tothe polymeric layer by a metallic electrical conductor 34 extending intothe polymeric layer at the first end.

Dielectric layer 22 may be formed by essentially any polymeric materialwhich can be etched by the etchants discussed below. Many of the commonorganic polymers normally used to form dielectric layers in electronicconnection components are susceptible to gaseous etchants. Polyimide canbe etched in this manner and can be used as the material of polymericlayer 22. In the particular embodiment depicted in FIGS. 1 and 2,polymeric layer 22 is provided as a single layer forming the entirety ofa supporting structure, and conductors 34 are vias extending entirelythrough that single layer structure. However, polymeric layer 22 can beprovided as part of a larger support structure. For example, thepolymeric layer may form one surface layer on a complex, multilayersupport structure incorporating numerous dielectric layers, electricallyconductive potential plane layers and layers of internal electricalconductors. Electrical conductors 34 need not extend entirely throughthe support structure. For example, the electrical conductors 34 mayextend into the interior of a complex support structure, and mayterminate at one or more of the internal conductors and/or potentialplane elements of such a complex structure.

The starting structure may be fabricated by essentially any conventionalprocess. For example, leads 54 may be formed by additive plating onpolymeric layer 22 or by subtractive etching of a preexisting metallayer in contact with the polymeric layer. Conductors 34 may be formedby conventional plating processes for forming the liners in polymericlayers. The processes used to form the leads desirably provide the leadswith good adhesion to the polymeric layer. For example, where the leadsare formed by additive plating, an initial layer of metal may bedeposited onto the polymeric layer by a high-energy deposition processsuch as sputtering, and the leads may be additively plated onto theinitial layer. A metal layer may be laminated to the polymeric layerusing conventional adhesives (not shown) and the metal layer may besubtractively etched to form the leads. The metal in leads 24 may beessentially any electrically conductive metal usable as an electricallead. For example, copper, gold and alloys containing these metals maybe employed. Moreover, leads 24 may include plural layers of differentmetals. For example, leads 24 formed from copper or copper alloy and maybe covered by a thin layer of gold. The particular leads illustrated inFIGS. 1 and 2 incorporate spots 36 of a bonding material at the secondend of each lead. Bonding material 36 is adapted to bond the second endsof the leads to contacts on a microelectronic component as discussedbelow. The dimensions and configurations of the leads may be generallyas described in the aforementioned '964 patent.

The first surface 26 bearing leads 24 is exposed to an etchant whichreacts with the polymer of layer 22 and erodes the polymer layer. Mostpreferably, the etchant is a gaseous etchant which reacts with thepolymer to form gaseous byproducts. The gaseous etchant desirably is aplasma of an oxidizing reactant gas mixture incorporating one or moreoxidizing moieties such as a halogen, oxygen or mixtures of halogens andoxygen. Such a plasma contains the oxidizing moieties in a highlyactivated state as, for example, as ions, radicals, molecules and atomswith electrons in high-energy, unstable or metastable states. Forexample, in an oxygen-containing plasma, oxygen commonly is present asmonatomic oxygen (O) and ozone (O₃). These species are formed morereactive than the normal, stable, diatomic form of oxygen (O₂). As usedin this disclosure with reference to a constituent of a gaseous etchant,the term “activated species” should be understood as referring to anyspecies of the constituent which is more reactive than the normal,stable form of such constituent. A plasma may be provided at firstsurface 26 by means of a conventional plasma treatment apparatus. Suchapparatus typically includes a chamber connected to a supply of theplasma-forming reactant gas mixture. Electrodes may be provided withinthe chamber for applying electrical energy directly to the gas mixturein the chamber. Alternatively or additionally, a coil or other suitableantenna may be disposed outside of the chamber for applying radiofrequency electrical energy through the wall of the chamber. The chamberis provided with exhaust pumps for maintaining the interior of thechamber under subatmospheric pressure and with conventionalpressure-regulating and energy-regulating devices. The electrical energyapplied to the gas mixture within the chamber produces an electricaldischarge and thus ionizes the gas mixture to form the plasma. In aso-called direct plasma process, the plasma is directly in contact withthe polymeric layer. In an indirect plasma process, the plasma is formedin a plasma region of the chamber remote from the structure to betreated. The gas flow within the chamber is arranged so that the gasflows through the plasma region and from the plasma region towards thestructure being treated. This arrangement can be used, for example,where the particular activated species formed in the plasma have anappreciable “half-life” and hence can survive in the flowing gas untilthey reach the structure being treated. In the indirect plasmatreatment, the structure is exposed to a mixture of activated speciesleft after passage of the gas through the plasma, commonly referred toas an “afterglow”, rather than to the plasma itself. Both direct andindirect plasma treatments are well known in the art of plasma treatmentand hence need not be further described herein.

During exposure to the gaseous etchant, the surface of structure 22opposite from surface 26 may be protected by a temporary mask layer 40.Mask layer may be a layer such as an adhesive-backed polymeric maskinglayer or an adhesive-bearing metallic layer such as a copper foil. Asthe gaseous etchant contacts surface 26, it reacts with the material ofthe polymer layer at such surface and converts the same to gaseousby-products which are swept from the chamber with the used reactant gas.The gaseous etchant does not appreciably attack the metal in the leads.The gaseous etchant attacks those portions of the exposed surface 26which are not covered by the leads and also attacks those portions ofthe polymeric layer surface beneath the leads, beginning at the edges ofthe leads. The etching process is generally isotropic. That is, theetched front advances at substantially equal rates in horizontal andvertical directions from the edges of the leads. Thus, surface 26recedes in the areas which are not covered by the leads and in the areasadjacent the edges of the leads. As the process progresses, the surfaceof polymer layer 22 is etched from beneath leads 24, starting at theedges of the leads.

The etching step is terminated when it has reached the stage depicted inFIGS. 3–7. At this stage of the process, etched regions advancing fromopposite edges 42 and 44 of the narrow, elongated sections 32 have metone another and joined with one another, so that the elongated sections32 of the leads are entirely detached from the etched surface 26′ of thepolymer layer 22. However, at the somewhat wider, second ends 30, theadvancing etch fronts have not yet met one another. Thus, a smallpolymeric region 46 remains beneath each second end 30. Each such region46 forms a connecting element which is smaller than the associatedsecond end region 30 of the lead. Each such connecting element extendsfrom the newly etched polymer surface 26′ to the lead, so that thesecond end 30 remains attached to the polymer layer, but verticallyspaced from the polymer layer. The first end 28 of each lead remainsattached to the polymer layer by the electrically conductive via 34.Depending upon the dimensions of the polymer layer and the dimensions ofthe via, a polymeric anchor connecting element 48 may also remain at thefirst end 28 of each lead.

When the etching process reaches the stage illustrated in FIGS. 3–7, thecomponent is ready for use. Because the etching step does not leave anyresidue on the component, and does not utilize liquid which must berinsed from the component, no further processing steps are required toclean residues or etching solutions from the component. Indeed, theetching step actually cleans organic contaminants from the metallicleads. The temporary masking layer 40 may be removed after the etchingprocess, as by peeling it away. Alternatively, masking layer 40 may beomitted if the polymeric layer is placed in the plasma chamber in such afashion that only the first surface 26 is exposed to the gaseousetchant. For example, the opposite surface of the polymeric layer maylie against a support, or may be covered by a protective blanket of aninert gas admitted during the process so that the inert gas flows overthe opposite surface and protects it from attack by the gaseous etchant.

The finished components, as illustrated in FIGS. 3–7, include leadshaving first ends or anchor portions 28 permanently attached to thepolymeric layer 22. The second end or attachment portion 30 of each leadis releasably connected to the polymeric layer by a polymeric connectingelement 46. Thus, connecting elements have only limited strength becauseit has a relatively small area. The strength of the connection betweeneach attachment section or second end 30 and the polymeric layer 22cannot exceed the tensile strength of the associated connecting element46. That tensile strength in turn is directly proportional to thecross-sectional area of the connecting element. Such cross-sectionalarea depends upon the dimensions of the second end 30, the rate ofetching and the etching time. All of these factors can be controlledreadily and repeatedly on a large scale.

The particular component discussed above with reference to FIGS. 1–7 isused in a process as described in the aforementioned '964 patent. Asdiscussed in greater detail therein, the connection component isjuxtaposed with a microelectronic chip, wafer or other microelectronicelement 50 (FIG. 8), so that the releasably connected second ends 30 ofthe leads are aligned with contacts 52 on the microelectronic element.Heat and pressure are applied to bond the second ends 30 of the leads tothe contacts 52 using the bonding material 36 carried by the leads.During this process, the second ends of the leads remain attached to thepolymeric layer by the connecting elements 46. After the second endshave been bonded to the contacts, the polymeric layer 22 andmicroelectronic element 50 are moved away from one another through apredetermined displacement so as to deform the elongated sections 32 ofthe leads to a vertically extensive disposition. As the microelectronicelement and dielectric layer move away from one another, the second endsof the leads move away from the surface 26′. The connecting elements 46either break or pull away from the surface of the metal leads. However,because the strength of each connecting element is well controlled, thesecond ends of the leads will release reliably from the polymeric layer.As further discussed in the '964 patent, a compliant material such as agel or elastomer may be provided around the deformed leads, as byintroducing a liquid encapsulant between the polymeric layer and thedielectric element and curing the liquid encapsulant. The verticallyextensive, bent leads provide flexible interconnections between the chipcontacts 62 and the electrical conductors 34 on the polymeric element.

In a process according to a further embodiment of the invention, leadswith elongated regions 132 and attachment regions or end regions 130 areprovided on a surface 126 of a polymeric layer 122. A mask 140 covers afirst region of the dielectric surface and covers those portions 133 ofthe leads exposed in this region. Mask 140 itself is susceptible toattack by the gaseous etchant. The etching step is performed asdiscussed above. In those regions of the surface which are not coveredby mask 140, surface 126 is attacked, leaving elongated portions 132detached from the newly etched surface 126′, and leaving end regions orattachment regions 130 connected to the newly etched surface 126′ bypolymeric connecting elements 146 similar to those discussed above. Inthe region of the polymeric layer initially covered by the mask, surface126 remains substantially unetched and hence lead portions 133 remainsecurely anchored to the unetched surface of layer 122. The mask isremoved by the etching process itself; the etching step is terminatedshortly after the mask is eroded away by the etchant. Alternatively,mask 223 may be resistant to the etchant, and may be physically peeledaway after the etching step. For example, mask 223 may include ametallic layer such as a layer of copper together with an adhesive.

The etching process forms a vertically-extensive step 127 in the surfaceof the polymeric layer at the juncture of the masked and unmaskedportions. Each elongated portion 132 projecting over the etched regionis spaced above the etched surface 126′ of the polymeric layer. Theleads may be plated after etching. For example, where the leads 132 areformed from a metal such as copper, a more fatigue-resistant, morebondable metal such as gold may be applied as a layer 137 around theleads. At least in those regions of the leads which are spaced from thepolymeric surface, the plating layer 137 may form a continuous jacketaround the entire lead, as seen in FIG. 11. The plating protects theleads from corrosion and fatigue and also provides a lower-impedancecomposite lead. The effect on lead impedance is particularly significantin the case of high-frequency signals, which tend to propagate along thesurfaces of the leads.

In a process according to a further embodiment of the invention, theleads 224 (FIG. 12) are of substantially uniform width. Here again, afirst region of the surface 226 and the corresponding anchor portions233 of the leads are covered by a mask 240. After etching, the exposedportions of leads 224 are connected to the etched polymeric surface 226′by polymeric connection elements 246 in the form of strips narrower thanthe leads. The mask-covered anchor regions 233 remain attached to theoriginal surface 226 over substantially the full widths of the leads.Thus, the anchor regions at the first ends of the leads remainpermanently attached whereas the exposed portions 230 at the second endsof the leads are releasably attached to the polymer layer by the narrowconnecting elements 246. In a further step, a slot 255 is cut throughthe polymer layer 222 beneath the leads, between the anchor regions 233and the ends of the exposed or releasably attached regions 230. Such aslot may be formed, for example, by a further etching step from theopposite surface of the polymer layer, or by laser ablation of thepolymer layer. Processes according to this aspect of the invention maybe used to make connection components for use in processes asillustrated in the aforementioned 94/03036 International Publication. Asdescribed in greater detail in that publication, the connectioncomponent can be used in a process wherein a bonding tool is advancedthrough the slot 255 and engaged with each lead so as to break the leadaway from the dielectric layer. During the process, the polymericconnecting element 230 associated with each lead is broken as that leadis engaged by the bonding tool and pushed away from the dielectricsupporting layer.

A method according to a further embodiment of the invention utilizes astarting structure incorporating a support substrate having a toppolymeric layer 322 and an electrically conductive potential plane orground plane layer 323 remote from the exposed surface 326 of the topdielectric layer. The starting structure also includes a furtherdielectric layer 325 on the rear or bottom side of potential plane layer323. Vias with conductive via liners 327 extend from the potential planelayer to the exposed surface 326 of the top dielectric layer 322.Numerous leads 324, of which only one is shown in FIG. 15, are providedon the exposed surface 326. Here again, each lead includes a first end328, a second end 330 and an elongated, narrow section 332 extendingbetween the first and second ends. Using process steps similar to thosediscussed above with reference to FIGS. 9 and 10, the exposed surface326 of the top dielectric layer is etched while a portion of the topsurface is covered by a mask (not shown). This leaves the structure inthe configuration depicted in FIG. 15, wherein an anchor section 333 ofeach lead adjacent the first end therein remains fully attached to theunetched surface 326, the second end 330 is connected to the etchedsurface 326′ of dielectric layer 322 only by a relatively narrow,frangible connecting element 346 formed during the etching process and apart of the elongated section 332 adjacent second end 330 is detachedfrom the newly-etched surface 326′ of the polymeric layer 322.

After the etching step, a mask is applied over the assembly. The maskhas an opening delineated by broken lines 339 in FIG. 15. The opening inthe mask encompasses most of elongated section 332, but stops short ofthe second end 330. In the next stage of the process, a conformalcoating 341 of a dielectric material is applied on those portions ofleads 324 disposed within the opening 339 of the mask. As depicted inFIG. 17, the conformal coating forms a continuous dielectric jacketsurrounding elongated lead portions 332. Some of the conformal coatingalso extends over a part of lead anchor regions 333 and merges with theunetched surface 326 of the dielectric top layer 322. The thickness ofcoating 341 is exaggerated in the drawings for clarity of illustration.In practice, the conformal coating desirably is about 0.0005 inches toabout 0.002 inches thick, i.e., about 12–50 μm thick. Thinner conformalcoatings can be employed. Also, the cross-sectional dimensions of theleads are exaggerated in the drawings. The elongated sections of theleads desirably have cross-sectional dimensions less than about 100microns. For example, the elongated sections of the leads may be about5–15 μm thick and about 15–50 μm wide.

The conformal coating may be applied by electrophoretic deposition. Inthe electrophoretic deposition process, leads 324 are connected to asource of an electrical potential and immersed in a bath of a liquiddeposition mixture. A counter-electrode is also immersed in thedeposition mixture. The potential applied by the source causes the solidmaterial from the deposition mixture to deposit onto the surfaces of theleads where the surfaces are not covered by the mask. To facilitateapplication of electrical potential to the leads, the leads may becontinuous with a bus (not shown) which is subsequently removed from thepart. Electrophoretic deposition processes and materials for use indeposition mixtures are well-known in the coating art. For example,materials for applying an acrylic polymer are sold under the designationPowercron cationic acrylic (700–900 series) by the PPG Company.Materials for applying epoxy coatings are sold under the designationPowercron cationic epoxy (400–600 series) by the same vendor. Thecounterelectrode desirably is considerably larger than the leads. Thecurrent density during the electrophoretic deposition step preferably ismaintained below about 1 milliampere per square centimeter of exposedlead surface so as to minimize bubble formation in the depositedcoating. The current may be maintained substantially constant during thedeposition process. The potential applied may be about 100 volts. Theprocess typically takes a few minutes. After the electrophoreticdeposition step, the part is removed from the bath, washed to removeclinging undeposited deposition solution and then baked to cure thecoating to a solid form.

Other processes for depositing the dielectric coating may be employedas, for example, dipping or spraying in a curable coating material suchas an epoxy, urethane, lacquer, or plastisol to form an adherent liquidfilm and then curing the liquid film to form the solid dielectric. Vapordeposition processes and plasma polymerization processes may also beemployed. The coating process which is used should be capable ofdepositing a thin coating on the unmasked area of the leads. It isdesirable to apply the coating in as close to a uniform thickness aspracticable.

After the dielectric coating is applied, the mask used duringapplication of the dielectric coating is removed and a further mask isapplied. The additional mask covers the component and the leads exceptthat in the area denoted by broken lines 355 in FIG. 16. Thus, theadditional mask has an opening slightly shorter than opening of the maskused for deposition of the dielectric coating in the lengthwisedirection along the elongated portions of the leads, so that the edgesof the additional mask opening fall within the portion of the leadcovered by dielectric coating 341. The opening in the additional maskalso extends to via liner 327. A continuous layer of an electricallyconductive material, preferably a metal such as copper or gold, isapplied within the opening of the additional mask so as to form ametallic coating 357 surrounding the dielectric layer 341 and theelongated portion 332 of each lead. Metal layer 357 has additionalportions 359 extending into electrical contact with via liner 327, sothat the metal layer is electrically connected to the internal groundplane 323 of the supporting structure. The metal layers may be formed byconventional metal deposition processes such as electroless plating orvapor deposition to deposit an initial, very thin film of metal,followed by electroplating to build up the metal to the final thicknessdesired. Because the metal coatings on all of the leads are electricallycontinuous with the ground plane 323, electroplating can be performed byapplying the necessary plating potential to the ground plane afterdeposition of the initial metal layer. Preferably, the metal layer isless than about 25 μthick, and most preferably about 12 μm thick orless.

The finished leads, as depicted in FIGS. 18 and 19, can be employed inthe same manner as the leads discussed above. Thus, the releasablesecond end 330 of each lead may be connected to a supporting substrateor other microelectronic component and may be bent away from dielectriclayer 322 and the remainder of the support structure. The elongatedportion 332 of each lead remains flexible. However, the elongatedportion of each lead is surrounded, over at least a part of its length,by dielectric layer 341 and by conductive layer 357, which is connectedto a constant potential on ground plane 323. This provides a controlledimpedance along the length of the lead. Moreover, the metallic shieldcoaxially surrounding each lead effectively blocks radiation ofelectromagnetic fields from or to the lead. This substantially reducesor eliminates cross-talk between adjacent leads and coupling ofelectromagnetic interference to the leads. Moreover, the polymeric layerand metallic layer mechanically reinforce each lead and reduce itssusceptibility to fatigue failure. The metal used in the outer layer orjacket 357 desirably has high fatigue resistance Gold or alloys commonlyreferred to as shape memory alloys, also known as “pseudoelastic alloys”or “superelastic alloys” may be employed. Such alloys include Nitinol™an alloy including nickel and titanium, and also include certain alloysof thallium and indium, as well as copper-aluminum-nickel alloys.

The metallic and dielectric jackets discussed above can be applied toleads having many different configurations. For example, one form ofconnection component depicted in International Publication WO 94/03036includes a dielectric support 422 having a gap 423 therein and pluralityof elongated leads 424 projecting from the support across the gap. Eachlead has a first end 428 extending along the top or first surface of thedielectric support 422 and permanently attached to the dielectricsupport on one side of the gap. Each lead also has a second end 430releasably connected to a metallic bus 431 by a frangible section 433,and hence releasably attached to the dielectric support 422. Typicalleads of this type have cross-sectional dimensions (width and thicknesstransverse to the direction of elongation of the leads) 50 microns wideor less, and commonly about 30 microns wide or less. As discussed ingreater detail in the '036 publication, these leads can be connected toa semiconductor chip or microelectronic element by engaging each lead424 with a bonding tool and forcing the lead downwardly, into gap 423 soas to break the frangible section 433 and detach the second end of thelead. The lead is thus bent downwardly and bonded to a contact (notshown) on the microelectronic element. A dielectric layer 441 and aconductive layer or jacket 457 similar to those discussed above withreference to FIGS. 16–19 may be applied around part of each lead 424.The metallic jackets 457 of the various leads may be contiguous with ametallic layer 459 extending downwardly along the edge of the gap andjoining with a ground plane 423 on the bottom surface of the dielectricelement. These leads may be formed by masking and deposition processessimilar to those discussed above.

The connection component depicted in FIG. 21 incorporates leads having adielectric jackets 541 and conductive jackets 557. The conductive jacketof each lead surrounds the elongated portion 528 of such lead along atleast a part of its length. Leads 528 merge with traces 529 on thedielectric element 520. The conductive jackets 557 of at least some ofthe leads are not connected to a common ground plane, but instead areconnected to additional traces 531 on the dielectric element. Theconnection component can be used with a microelectronic element such asa semiconductor chip 550 having contacts 551 disposed in pairs. When thetip end 530 of the lead is connected to one contact of a pair, theconductive jacket 557 is connected to the other contact of the pair. Forexample, lead tip end 530 a is connected to contact 551 a, whereas theconductive jacket 557 a of the same lead is connected to contact 551 bof the same contact pair. As depicted in FIG. 21, lead tip end 530 b andthe associated conductive jacket 557 b have not yet been connected tothe microelectronic element. These parts will be connected to contacts551 c and 551 d. To facilitate connection of the jacket, the contactassociated with the lead tip end (the contact which does not engage thejacket), such as contact 551 a, may project upwardly from the topsurface of the microelectronic element. For example, such a contact canbe provided with a solder ball of other mass of electrically conductivematerial. Also, the conductive jackets may be formed from a readilybondable material or overplated with a bondable material in the regionof the jacket adjacent the tip end of the lead. For example, materialssuch as solders, eutectic bonding alloys, conductive polymercompositions and gold can be used. Similarly, the contacts which engagethe conductive jackets may be provided with bonding material adapted tobond readily with the material of the jacket. Thus, contacts 551 a and551 b may be provided with different bonding materials or with the samebonding material, depending upon the composition of the lead itself andthe composition of the conductive jacket. The bonding materials may beheat-actuated, so that the conductive jackets can be bonded to theassociated contacts without the need to apply sonic or other vibrationalenergy through the lead and through the polymeric jackets.

The connected conductive jackets serve to connect contacts on themicroelectronic element with traces on the dielectric element. Thus,conductive jacket 557 a electrically connects contact 551 b and trace531 a. These conductive paths extend in parallel with the conductivepaths provided by the leads themselves.

The parallel conductive paths provided by the jackets can be employed ina differential-signal arrangement. As schematically indicated in FIG.22, a device, such as a device 570 may be arranged to send signals to asecond device 572 through two conductors 574 and 576 extending alongsideof one another. Device 570 is arranged to transmit signals by varyingthe difference in potential applied to the two conductive paths, mostpreferably by applying equal but opposite-sense signals to the twoconductive paths. For example, device 570 may extend a first digitaloutput state by applying a relatively high voltage along path 574 and alow voltage along path 576, and may signal the opposite digital outputstate by applying a high voltage on path 576 and a low voltage on path574. Stated another way, device 570 sends one signal on path 574 andsends an inverted version of the same signal on path 576. Device 572subtracts the two signals supplied on paths 574 and 576 to derive aninput signal.

Preferably, the connections are arranged so that the two paths used ineach differential connection include a lead and the conductive jacketassociated with that lead. For example, path 574 shown in FIG. 22 mayinclude contact 551 a, lead 528 a and trace 529 a, whereas the otherpath 576 used in the same differential connection incorporates contact551 b, jacket 557 a which surrounds lead 528 a and trace 531 a whichextends adjacent to trace 529 a on the dielectric element. In thisarrangement, the two paths constituting each differential connectionextend alongside one another throughout the entire route starting withthe contacts 551 of the microelectronic element. This arrangementprovides substantial immunity to electromagnetic interference. Use ofleads which provide dual conductive paths in a differential connectionis discussed in greater detail in the co-pending, commonly assigned U.S.patent application of Joseph Fjelstad and John W. Smith entitled,Microelectronic Lead Structures With Plural Conductors, filed on evendate herewith, now U.S. Pat. No. 6,239,384, the disclosure of which ishereby incorporated by reference herein. Also, the various leadsdescribed herein may be used as connecting leads in a chip whereininternal signals are routed from one place in the chip to another placein the chip through an external connecting element. Structures of thistype are described in the aforementioned application of Joseph Fjelstadand John W. Smith filed on even date herewith, and are also described inco-pending, commonly assigned U.S. Provisional Patent Applications60/042,187, filed Apr. 2, 1997, and 60/063,954, filed Oct. 31, 1997, thedisclosures of which are hereby incorporated by reference herein.

In yet another variant, some or all of the conductive jackets may beconnected between a potential plane such as a ground or power plane onthe support structure and corresponding contacts on the chip, such asground or power input contacts. In a still further variant, each leadmay be provided with a plurality of conductive jackets and a pluralityof dielectric jackets, so that a first dielectric jacket is disposedbetween the lead and an inner conductive jacket whereas a seconddielectric jacket is disposed between the inner conductive jacket and anouter conductive jacket. The various conductive jackets can be used assignal carrying conductors or as constant potential conductors asdiscussed above.

In a process according to yet another embodiment of the invention, leads624 (FIG. 23) have elongated sections 632 of substantially uniformwidth, each such elongated section being connected to an anchor region628. Here again, the anchor regions of the leads may be electricallyconnected to other electrically conductive structures on dielectricelement 620 by conductive elements 629 extending to the anchor regions.Here again, the dielectric layer 620 is exposed to an etchant whichremoves a polymeric material of the dielectric layer. As discussed abovein connection with FIGS. 12–14, this leaves an elongated, web-likepolymeric connecting element 646 extending along the length of elongatedsection 632 of the lead, as well as a further polymeric connectingelement 647 underlying the anchor region 628. Thus, the web-likeconnecting element 646 extends from the anchor region almost to the tipend 630 of the lead. The web-like connecting element is narrower thanthe elongated section of the lead. It extends vertically between theetched surface and the underside of the lead.

In use, the tip end 630 may be bonded to a contact on a microelectronicelement 650. As the microelectronic element and polymeric layer arepulled away from one another, the connecting element 646 separatesprogressively along its length and along the length of the lead, so thatthe lead progressively peels away from the polymeric layer as themicroelectronic element 650 and tip end 630 move through the positionshown in solid lines in FIG. 24 to the position illustrated in brokenlines at 630′, 650′. Separation of the polymeric connecting element mayoccur by tearing of the polymeric web-like connecting element itself, asdepicted in FIG. 24, leaving a part of the polymeric connecting elementwith the lead and a part with the polymeric layer. Alternatively, thepolymer may break at the juncture of the connecting element and thepolymeric layer, so that the entire connecting element remains with thelead. More commonly, the polymeric connecting element will peel awayfrom the metallic lead, so the entire connecting element remains withthe polymeric layer. Various forms of these release mechanisms may occurat different locations along the length of a single lead. Whicheverrelease mechanism occurs, however, the lead will be peeled progressivelyaway from the polymeric layer.

Progressive peeling as described with reference to FIGS. 23–24 may beapplied to leads of different configurations. For example, the leadsdepicted in FIGS. 1–8 may be provided with elongated web-like connectingelements extending along the curved elongated sections 32, in additionto the small columnar connecting elements 46 at the tip ends, byterminating the etching process before erosion of the polymer beneaththe elongated sections is complete. The web-like connecting element maybe contiguous with the columnar connecting element.

Many other variations and combinations of the foregoing features may beemployed. For example, the dielectric and metallic layers as discussedwith reference to FIG. 20 can be provided on flexible leads which aresupported at only one end by the dielectric support structure. Thus, thedielectric and metallic layers can be employed on leads of conventionaltape automated bonding (“TAB”) structures. Also, etchants other than thegaseous etchants discussed above can be employed. For example,conventional liquid etchants can be used to etch the polymeric layer.Also, the etching process can be controlled so that the elongatedportions of the leads are not entirely detached from the polymericlayer, but instead remain attached to the polymeric layer by narrow,elongated web-like polymeric connecting elements extending lengthwisealong the elongated portions. These web-like polymeric connectingelements can be torn progressively as the elongated portions of theleads are peeled away from the polymeric layer.

As these and other variations and combinations of the features discussedabove can be utilized without departing from the present invention, theforegoing description of the preferred embodiments should be taken byway of illustration rather than by way of limitation of the invention asdefined by the claims.

1. A method of making microelectronic connection components comprisingthe steps of: (a) providing a support structure including a dielectriclayer defining an edge and one or more leads, the leads having anchorregions extending along the dielectric layer and having elongatedsections extending beyond the edge; and (b) depositing a dielectricmaterial on said leads electrophoretically so that the depositeddielectric material surrounds at least one of said elongated sections ofsaid leads over at least a portion of the length of such section.
 2. Amethod as claimed in claim 1 wherein each said lead has a first end onsaid dielectric layer connected to anchor region of the lead and asecond end connected to the elongated section of such lead and saiddepositing step is performed so as to leave the first ends of at leastsome of said leads uncovered by the dielectric material.
 3. A method asclaimed in claim 2 wherein said depositing step is performed so as toleave the second ends of at least some of said leads uncovered by thedielectric material.
 4. A method as claimed in claim 1 wherein thedielectric layer has a gap therein, said edge bounds the gap, and saidelongated sections of the leads extend across the gap, said depositingstep including depositing the dielectric material onto portions of saidelongated sections of the leads extending across the gap.
 5. A method asclaimed in claim 1 wherein the depositing step includes depositing thedielectric material so that the dielectric material extends across saidedge and contacts the dielectric layer.
 6. A method as claimed in claim1 wherein said portions of said elongated sections extending beyond saidedge are movable with respect to said support structure.
 7. A method asclaimed in claim 1 wherein said step of depositing said dielectricmaterial is performed so that said deposited dielectric materialentirely surrounds said elongated sections at least some locations.
 8. Amethod as claimed in claim 7 further comprising the step of depositingan electrically conductive material over said deposited dielectricmaterial so that said deposited conductive material forms referenceconductors surrounding and extending coaxially with said elongatedsections of said leads and insulated therefrom by said depositeddielectric material.
 9. A method as claimed in claim 1 furthercomprising the step of depositing an electrically conductive materialover said deposited dielectric material so that said depositedconductive material forms reference conductors extending along with saidelongated sections of said leads and insulated therefrom by saiddeposited dielectric material.
 10. A method of making microelectronicconnection components comprising the steps of: (a) providing a supportstructure and one or more leads, each said lead having a first end onsaid support structure, a second end and an elongated section extendingalong the support structure from the first end of the lead toward thesecond end of the lead; and (b) depositing a dielectric material on saidleads electrophoretically so that the deposited dielectric materialsurrounds at least one of said elongated sections over a portion of itslength without depositing the dielectric material on the first ends ofthe leads.
 11. A method as claimed in claim 10 wherein the depositingstep is performed without depositing the dielectric material on thesecond ends of the leads.